The use of partially permeable materials, e.g., impregnated or waxed paper, plastics, etc., presents a novel problem in the packaging of perishable commodities, such as edible oils and fats, other foods, carbonated beverages, wine and beer, and also of other materials that are affected by continuing exposure to air and airborne substances, or endangered by the loss of constituents, as, for example, in the case of carbon dioxide loss from carbonated beverages or aroma loss in spiced consumables. The problem derives from the fact that, in contrast to the materials customarily used for packaging under such conditions, namely glass and metal, these partially permeable materials do not provide absolute protection because they are never completely impervious.
The art has developed materials that are relatively impervious to given substances. These "better" materials tend to be more expensive, and despite the added cost even they have a finite permeability.
A typical instance is that of plastics which will be used as illustrative, although similar examples from the field of paper packaging, for example, could also be used. In the instance of plastics the approach taken heretofore was to develop barrier polymers with better permeation impedance for specific substances, such as oxygen, carbon dioxide, water vapor, aromatics, etc. These efforts did meet with considerable success. Thus, for example, the permeation rate of oxygen was reduced by a factor of several orders of magnitude from polystyrene to the newly developed acrylonitrile copolymers, or to terephthalic polyesters. Nevertheless, a definite amount of permeation remains even in the best plastic due to the molecular arrangement thereof.
As a result, a new factor has to be introduced whenever it was desired to package perishables in plastic or other partially permeable materials, namely shelf-life. While a metal can or glass jar will keep its contents unchanged for a practically indefinite period, a time limit, mostly in terms of weeks, has to be prescribed for the plastics, modified paper, etc.
Accordingly, it is a principal object of the present invention to provide a novel material having improved resistance to permeation, especially gas permeation.
It is a further object of the present invention to provide a material as aforesaid which utilizes a partially permeable barrier material and which significantly increases its resistance to gas permeation.
It is a still further object of the present invention to inexpensively and conveniently provide a material as aforesaid.
Further objects and advantages of the present invention will appear hereinafter.